A number of polymers are capable of being crosslinked in the presence of a catalyst. A significant improvement in physical and chemical properties of such polymers occurs when such polymers are subjected to a crosslinking process. However, crosslinked polymers become highly viscous as a result of their increased molecular weight, which occurs due to the crosslinking process. As a result, crosslinked polymers are typically incapable of being molded into desired shapes or are incapable of being readily applied over substrate surfaces as a layer.
Thus, a catalyst is stored separately from a polymer or a polymeric component of a coating composition, which contains the polymer. Just before use the catalyst is mixed with the polymeric component to form a pot mix which can then be readily applied as a layer by conventional means, such as by brushing or spraying, over the surfaces of substrates or can be readily shaped into an article by conventional means, such as molding. The polymers in the layer then crosslink in the presence of the catalyst to form a coating on the surface having improved physical and chemical properties, such as durability, water and solvent resistance, mar resistance, block resistance compared to the uncrosslinked polymer.
Several types of catalysts are known to crosslink a polymer. For example, it is conventional to use a heavy metal catalyst, such as a tin compound, for crosslinking polymers having oxidatively crosslinkable functionalities. However, these metal catalysts tend to have a low catalytic activity. As a result, a significantly higher quantity of such catalysts, generally in amounts exceeding 5000 parts per million (ppm) or in excess of 0.5 weight percent based on the total polymer solids weight, have to be added to the polymer for achieving a desired degree of crosslinking of the polymer. Moreover, these metal catalysts have adverse impact on the environment because they are hazardous to human, animal and plant habitat. Furthermore, these heavy metal catalysts cannot be readily degraded into harmless compounds. Thus, articles made from polymers containing these heavy metal catalysts or articles coated with coating compositions containing these heavy metal catalysts cannot be safely disposed of in typical land fills or other disposal sites, unless such catalysts are removed or rendered harmless before disposal. The present invention solves this problem by providing for an oxidative catalyst that has no substantially adverse impact on the environment and it readily undergoes biodegradation upon disposal. As a result, the catalyst of the present invention can be safely disposed of in conventional landfills or disposal sites without any significant impact on the environment. Furthermore, as the catalyst of the present invention is catalytically more active than conventional heavy metal catalysts, smaller amounts of the catalyst of the present invention are needed to achieve the same degree of crosslinking that is accomplished by utilizing higher amounts of conventional heavy metal catalysts.